Development of a Rat Plasma and Brain Extracellular Fluid Pharmacokinetic Model for Bupropion and Hydroxybupropion Based on Microdialysis Sampling, and Application to Predict Human Brain Concentrations.

Administration of bupropion [(±)-2-(tert-butylamino)-1-(3-chlorophenyl)propan-1-one] and its preformed active metabolite, hydroxybupropion [(±)-1-(3-chlorophenyl)-2-[(1-hydroxy-2-methyl-2-propanyl)amino]-1-propanone], to rats with measurement of unbound concentrations by quantitative microdialysis sampling of plasma and brain extracellular fluid was used to develop a compartmental pharmacokinetics model to describe the blood-brain barrier transport of both substances. The population model revealed rapid equilibration of both entities across the blood-brain barrier, with resultant steady-state brain extracellular fluid/plasma unbound concentration ratio estimates of 1.9 and 1.7 for bupropion and hydroxybupropion, respectively, which is thus indicative of a net uptake asymmetry. An overshoot of the brain extracellular fluid/plasma unbound concentration ratio at early time points was observed with bupropion; this was modeled as a time-dependent uptake clearance of the drug across the blood-brain barrier. Translation of the model was used to predict bupropion and hydroxybupropion exposure in human brain extracellular fluid after twice-daily administration of 150 mg bupropion. Predicted concentrations indicate that preferential inhibition of the dopamine and norepinephrine transporters by the metabolite, with little to no contribution by bupropion, would be expected at this therapeutic dose. Therefore, these results extend nuclear imaging studies on dopamine transporter occupancy and suggest that inhibition of both transporters contributes significantly to bupropion's therapeutic efficacy.

Prediction of brain clozapine and norclozapine concentrations in humans from a scaled pharmacokinetic model for rat brain and plasma pharmacokinetics.

BACKGROUND: Clozapine is highly effective in treatment-resistant schizophrenia, although, there remains significant variability in the response to this drug. To better understand this variability, the objective of this study was to predict brain extracellular fluid (ECF) concentrations and receptor occupancy of clozapine and norclozapine in human central nervous system by translating plasma and brain ECF pharmacokinetic (PK) relationships in the rat and coupling these with known human disposition of clozapine in the plasma. METHODS: Unbound concentrations of clozapine and norclozapine were measured in rat brain ECF using quantitative microdialysis after subcutaneous administration of a 10 mg/kg single dose of clozapine or norclozapine. These data were linked with plasma concentrations obtained in the same rats to develop a plasma-brain ECF compartmental model. Parameters describing brain ECF disposition were then allometrically scaled and linked with published human plasma PK to predict human ECF concentrations. Subsequently, prediction of human receptor occupancy at several CNS receptors was based on an effect model that related the predicted ECF concentrations to published concentration-driven receptor occupancy parameters. RESULTS: A one compartment model with first order absorption and elimination best described clozapine and norclozapine plasma concentrations in rats. A delay in the transfer of clozapine and norclozapine from plasma to the brain ECF compartment was captured using a transit compartment model approach. Human clozapine and norclozapine concentrations in brain ECF were simulated, and from these the median percentage of receptor occupancy of dopamine-2, serotonin-2A, muscarinic-1, alpha-1 adrenergic, alpha-2 adrenergic and histamine-1 for clozapine, and dopamine-2 for norclozapine were consistent with values reported in the literature. CONCLUSIONS: A PK model that relates clozapine and norclozapine disposition in rat plasma and brain, including blood-brain barrier transport, was developed. Using allometry and published human plasma PK, the model was successfully translated to predict clozapine and norclozapine concentrations and accordant receptor occupancy of both agents in human brain. These predicted exposure and occupancy measures at several receptors that bind clozapine may be employed to extend our understanding of clozapine's complex behavioral effects in humans.

Cost-effectiveness analysis of a first-trimester screening test for preterm preeclampsia in the Netherlands.

OBJECTIVES: The risk of preterm preeclampsia (PT PE) can significantly be reduced by starting acetylsalicylic acid ≤ 16 weeks of gestational age. First trimester predictive models based on maternal risk factors to effectively start this therapy lacked sufficient power, but recent studies showed that these models can be improved by including test results of biochemical and/or -physical markers. To investigate whether testing a biochemical marker in the first trimester is cost-effective in the Netherlands, a cost-effectiveness analysis was performed in this study. STUDY DESIGN: The outcome of this study was expressed as an incremental cost-effectiveness ratio (ICER) with as effect prevented PT PE cases. To evaluate the impact of each model parameter and to determine model uncertainties, both univariate and probabilistic sensitivity analyses were performed. RESULTS: When compared to the baseline strategy, the test strategy is estimated to save almost 4 million euros per year on a national scale and at the same time this would prevent an additional 228 PT PE cases. The sensitivity analyses showed that the major drivers of the result are the costs to monitor a high-risk pregnancy and the specificity and that most of the model simulations were in the southeast quadrant: cost saving and more prevented complications. CONCLUSIONS: This study showed that a first-trimester test strategy to screen for PT PE in the first trimester is potentially cost-effective in the Dutch healthcare setting. The fact that the specificity is a major driver of the ICER indicates the importance for a (new) screening model to correctly classify low-risk pregnancies.

Early pregnancy biomarker discovery study for spontaneous preterm birth.

(1) OBJECTIVE: discover new candidate biomarkers for spontaneous preterm birth in early pregnancy samples. When fully clinically validated, early pregnancy biomarkers for sPTB give the possibility to intervene or monitor high-risk pregnancies more intensively through, as example, pelvic exams, ultrasound or sonographic cervical length surveillance. (2) STUDY DESIGN: Early pregnancy serum samples of eight spontaneous extreme and very preterm birth cases (<32 weeks of gestational age) without any symptoms of preeclampsia and fetal growth restriction and eight uncomplicated pregnancies were analyzed by liquid chromatography mass spectrometry (LC-MS). Thirteen proteins, which were differentially expressed according to the LC-MS data, were subsequently selected for confirmation by enzyme-linked immunosorbent assay (ELISA). (3) RESULTS: Differential expression of four candidate biomarkers was confirmed by ELISA with decreased early pregnancy levels of gelsolin and fibulin-1 and increased levels of c-reactive protein and complement C5 in the preterm birth group. (4) CONCLUSIONS: The confirmed candidate biomarkers are all to some extent related to inflammatory pathways and/or the complement system. This supports the hypothesis that both play a role in extreme and very preterm birth without any symptoms of preeclampsia and fetal growth restriction. The predictive value of complement C5, c-reactive protein, fibulin-1 and gelsolin should, therefore, be validated in another cohort with early pregnancy samples.

Microdialysis evaluation of clozapine and N-desmethylclozapine pharmacokinetics in rat brain.

A significant barrier to realization of the full potential of clozapine as a therapeutic agent in the treatment of schizophrenia is the substantial interpatient variability that exists along the therapeutic continuum of no response-efficacious response-adverse response. Genetic polymorphisms that manifest as highly variable pharmacodynamic and pharmacokinetic measures are its expected causes. To support investigations that seek to understand these causes, the plasma and central nervous system pharmacokinetics of clozapine were determined in rats, the latter using microdialysis sampling. Results obtained with clozapine and N-desmethylclozapine, a pharmacologically active human metabolite that was administered to a separate group of animals, support a conclusion of net carrier-mediated efflux of both compounds across the blood-brain barrier. These results are supported by the replication of published findings regarding the passive transport and net efflux transport of two model compounds, escitalopram and risperidone, respectively. The results obtained with clozapine and N-desmethylclozapine are considered a first step in the development of preclinical pharmacokinetic-pharmacodynamic models that will support deeper mechanistic studies of clozapine in in vivo pharmacology, as well as the development of translational models that augment pharmacogenetic investigations that seek to improve the safety and efficacy of clozapine therapeutic intervention in the treatment of schizophrenia.

First trimester serum biomarker discovery study for early onset, preterm onset and preeclampsia at term.

INTRODUCTION: Preeclampsia (PE) is a heterogeneous syndrome during pregnancy and postpartum and it is subdivided in this study into early onset (<34 weeks), preterm onset (34-37 weeks) and PE at term (>37 weeks). First trimester models currently lack a sufficient power to predict PE, but inclusion of biochemical markers shows an improvement of their predictive power. The aim of this study was to perform a biomarker discovery study in order to find possible novel first trimester biomarkers for each PE subtype. Further, our findings were related to available literature and the possible role of the proteins in the development of preeclampsia was discussed. METHODS: In this study, 9 early onset (<34 weeks), 8 preterm onset (34-37 weeks), 6 PE at term (>37 weeks) and 23 control samples were drawn between 11 and 14 weeks gestational age. Serum samples were prepared for liquid chromatography mass spectrometry analysis and protein data were exported for statistical analyses. All differentially expressed proteins were further evaluated by searching literature in MEDLINE, Embase and Web of science and differential expression of two proteins, which were not yet associated with PE, was verified through enzyme-linked immunosorbent assay (ELISA). RESULTS: After statistical analysis, six, four and eight proteins were differently expressed in early onset, preterm onset and PE at term, respectively. After exclusion of antibody fragments, only nine proteins remained. Seven out of these nine proteins were already in literature associated with preeclampsia and only three of them were described as differentially expressed in the first trimester or early second trimester of preeclamptic pregnancies. Differential expression of Apolipoprotein D (ApoD), which was not yet associated with PE, was confirmed by ELISA in both early and preterm onset PE in the first trimester. DISCUSSION: In this study, two main observations were made. First, some of the differentially expressed proteins have a role in the same biological pathway, such as the acute phase response or endometrium receptivity, and their differential expression was observed in all three PE subtypes. This observation supports the hypothesis that classification of PE could be more accurate when subtyping is based on the etiology and/or phenotype instead of the arbitrary parameter gestational age at onset or delivery. Second, seven differential expressed proteins were already associated in literature with preeclampsia, but this association was for only three of them observed in the first trimester. In addition, ApoD was not yet associated with PE in other studies and, moreover, its differential expression was confirmed by ELISA. Therefore the predictive power of these proteins in the first trimester is worth evaluating in a larger and more heterogeneous cohort.

Healthy and preeclamptic pregnancies show differences in Guanylate-Binding Protein-1 plasma levels.

The large interferon-inducible anti-angiogenic pro-inflammatory GTPase Guanylate Binding Protein-1 (GBP-1) is produced and secreted by activated endothelial cells and is highly induced by inflammatory cytokines and inhibited by angiogenic growth factors. During pregnancy a generalized mild inflammatory response is observed. During preeclampsia this generalized inflammatory response is even further activated and activation of the endothelium occurs. We hypothesized that GBP-1 is increased in healthy pregnancy and will be even further increased during preeclampsia. In the first experiment, plasma and placentas were collected from healthy and preeclamptic pregnancies. Plasma was also collected from non-pregnant women. For the second experiment longitudinal blood samples from women with a healthy or preeclamptic pregnancy were collected from the end of the first trimester until birth and one sample postpartum. The plasma GBP-1 levels were measured by ELISA and GBP-1 mRNA and protein levels in the placenta were tested by qPCR and immunohistochemistry. During pregnancy higher plasma concentrations of GBP-1 compared with non-pregnant women were observed. Surprisingly, during preeclampsia, plasma GBP-1 levels were lower than in control pregnancies and similar to the level of non-pregnant controls. Placental GBP-1 mRNA levels were not different between healthy and preeclamptic pregnancies and GBP-1 protein was virtually undetectable in the trophoblast by immunohistochemistry in placental tissue. Evaluation of longitudinal samples showed that plasma GBP-1 concentrations increased towards the end of pregnancy in healthy pregnancies, but not in preeclampsia. In line with our hypothesis, we found higher GBP-1 plasma levels during healthy pregnancy. However, plasma GBP-1 did not further increase during preeclampsia, but was stable. Further studies are needed to evaluate why GBP-1 does not increase during preeclampsia.

Oxazepam and temazepam attenuate paroxetine-induced elevation of serotonin levels in guinea-pig hippocampus.

Selective serotonin (5-HT) reuptake inhibitors (SSRIs) are used as a first-line treatment in depression. However, many depressed patients are also treated with benzodiazepines to alleviate increased anxiety and sleep disturbances normally associated with depression. Since benzodiazepines inhibit 5-HT neuronal firing activity, they might attenuate SSRI-induced increase in extracellular 5-HT levels. This study aimed to assess, using in-vivo microdialysis, the effects of the benzodiazepines oxazepam or temazepan on the SSRI paroxetine-induced 5-HT increase in the hippocampus of freely moving guinea-pigs. It was found that the acute systemic administration of paroxetine increased extracellular 5-HT levels. Pre-administration of oxazepam or temazepam significantly diminished the paroxetine-induced elevation of extracellular 5-HT levels (from 350% to 200% of baseline). It was concluded that benzodiazepines attenuate the ability of SSRIs to elevate hippocampal 5-HT levels. Thus, co-administration of benzodiazepines might affect the therapeutic efficacy of SSRI treatment.

Acute and repeated flibanserin administration in female rats modulates monoamines differentially across brain areas: a microdialysis study.

INTRODUCTION: Hypoactive sexual desire disorder (HSDD) is defined as persistent lack of sexual fantasies or desire marked by distress. With a prevalence of 10% it is the most common form of female sexual dysfunction. Recently, the serotonin-1A (5-HT(1A)) receptor agonist and the serotonin-2A (5-HT(2A)) receptor antagonist flibanserin were shown to be safe and efficacious in premenopausal women suffering from HSDD in phase III clinical trials. AIM: The current study aims to assess the effect of flibanserin on neurotransmitters serotonin (5-HT), norepinephrine (NE), dopamine (DA), glutamate, and gamma-aminobutyric acid (GABA) in brain areas associated with sexual behavior. METHODS: Flibanserin was administered to female Wistar rats (280-350 g). Microdialysis probes were stereotactically inserted into the mPFC, NAC, or MPOA, under isoflurane anesthesia. The extracellular levels of neurotransmitters were assessed in freely moving animals, 24 hours after the surgery. MAIN OUTCOME MEASURES: Dialysate levels of DA, NE, and serotonin from medial prefrontal cortex (mPFC), nucleus accumbens (NAC), and hypothalamic medial preoptic area (MPOA) from female rats. RESULTS: Acute flibanserin administration decreased 5-HT and increased NE levels in all tested areas. DA was increased in mPFC and MPOA, but not in the NAC. Basal levels of NE in mPFC and NAC and of DA in mPFC were increased upon repeated flibanserin administration, when compared to vehicle-treated animals. The basal levels of 5-HT were not altered by repeated flibanserin administration, but basal DA and NE levels were increased in the mPFC. Glutamate and GABA levels remained unchanged following either repeated or acute flibanserin treatment. CONCLUSIONS: Systemic administration of flibanserin to female rats differentially affects the monoamine systems of the brain. This may be the mechanistic underpinning of flibanserin's therapeutic efficacy in HSDD, as sexual behavior is controlled by an intricate interplay between stimulatory (catecholaminergic) and inhibitory (serotonergic) systems.

Microfiltration sampling in rats and in cows: toward a portable device for continuous glucocorticoid hormone sampling.

To monitor temporal patterns of glucocorticoids hormones in living animals, most often blood samples are collected. Blood sampling is invasive and subjects may find it--in particular--unpleasant when multiple samples are collected. We have developed a microfiltration collection device (MCD) sampling continuously, pulse-free, over a selected period of time, with minimum invasiveness as the device is inserted with only one venipuncture. The MCD consists of a hollow fiber membrane (probe), capillary collection coil and flow creator. Three biocompatible hollow fiber membranes were assessed on flow rate in rats, by placing the probe intraperitoneally, subcutaneously, or intravascularly and with or without heparin coating. The probe made from polyethylene coated with ethylene vinyl alcohol-heparin conveyed the best results and had the most benefit of the heparin coating. Consequently this probe was built into a collection device and tested in cows, sampling blood microfiltrate. Cortisol (protein-bound and -free) could be monitored in cows over a period of 7 hours. This device has several major advantages compared to manual blood collection: minor stress is induced by the application of the device; it has a low weight and can therefore be used in freely active subjects being in their own surroundings. The device can be sterilized and manufactured as a disposable tool, and the filled MCD can be shipped by regular mail to a specialized laboratory facility for analysis.

First trimester secreted Frizzled-Related Protein 4 and other adipokine serum concentrations in women developing gestational diabetes mellitus.

BACKGROUND: The aim of this study was to evaluate whether soluble frizzled-related protein 4 (sFRP4) concentration in the first trimester of pregnancy is individually, or in combination with Leptin, Chemerin and/or Adiponectin, associated with the development of gestational diabetes (GDM). METHODS: In a nested case-control study, 50 women with GDM who spontaneously conceived and delivered a live-born infant were matched with a total of 100 uncomplicated singleton control pregnancies based on body mass index (± 2 kg/m2), gestational age at sampling (exact day) and maternal age (± 2 years). In serum samples, obtained between 70-90 days gestational age, sFRP4, Chemerin, Leptin and Adiponectin concentrations were determined by ELISA. Statistical comparisons were performed using univariate and multi-variate logistic regression analysis after logarithmic transformation of the concentrations. Discrimination of the models was assessed by the area under the curve (AUC). RESULTS: First trimester sFRP4 concentrations were significantly increased in GDM cases (2.04 vs 1.93 ng/ml; p<0.05), just as Chemerin (3.19 vs 3.15 ng/ml; p<0.05) and Leptin (1.44 vs 1.32 ng/ml; p<0.01). Adiponectin concentrations were significantly decreased (2.83 vs 2.94 ng/ml; p<0.01) in GDM cases. Further analysis only showed a weak, though significant, correlation of sFRP4 with Chemerin (R2 = 0.124; p<0.001) and Leptin (R2 = 0.145; p<0.001), and Chemerin with Leptin (R2 = 0.282; p<0.001) in the control group. In a multivariate logistic regression model of these four markers, only Adiponectin showed to be significantly associated with GDM (odds ratio 0.12, 95%CI 0.02-0.68). The AUC of this model was 0.699 (95%CI 0.605-0.793). CONCLUSION: In the first trimester of pregnancy, a multi-marker model with sFRP4, Leptin, Chemerin and Adiponectin is associated with the development of GDM. Therefore, this panel seems to be an interesting candidate to further evaluate for prediction of GDM in a prospective study.

Antagonism of 5-HT(1A) receptors uncovers an excitatory effect of SSRIs on 5-HT neuronal activity, an action probably mediated by 5-HT(7) receptors.

Both microdialysis and electrophysiology were used to investigate whether another serotonin (5-HT) receptor subtype next to the 5-HT(1A) autoreceptor is involved in the acute effects of a selective serotonin reuptake inhibitor on 5-HT neuronal activity. On the basis of a previous study, we decided to investigate the involvement of the 5-HT(7) receptors. Experiments were performed with the specific 5-HT(7) antagonist SB 258741 and the putative 5-HT(7) agonist AS19. In this study WAY 100.635 was used to block 5-HT(1A) receptors. Systemic administration of SB 258741 significantly reduced the effect of combined selective serotonin reuptake inhibitor and WAY 100.635 administration on extracellular 5-HT in the ventral hippocampus as well as 5-HT neuronal firing in the dorsal raphe nucleus. In the microdialysis study, co-administration of AS19 and WAY 100.635 showed a biphasic effect on extracellular 5-HT in ventral hippocampus, hinting at opposed 5-HT(7) receptor mediated effects. In the electrophysiological experiments, systemic administration of AS19 alone displayed a bell-shaped dose-effect curve: moderately increasing 5-HT neuronal firing at lower doses while decreasing it at higher doses. SB 258741 was capable of blocking the effect of AS19 at a low dose. This is consistent with the pharmacological profile of AS19, displaying high affinity for 5-HT(7) receptors and moderate affinity for 5-HT(1A) receptors. The data are in support of an excitatory effect of selective serotonin reuptake inhibitors on 5-HT neuronal activity mediated by 5-HT(7) receptors. It can be speculated, that the restoration of 5-HT neuronal firing upon chronic antidepressant treatment, which is generally attributed to desensitization of 5-HT(1A) receptors alone, in fact results from a shift in balance between 5-HT(1A) and 5-HT(7) receptor function.

Do selective serotonin reuptake inhibitors acutely increase frontal cortex levels of serotonin?

Selective serotonin uptake inhibitors (SSRIs) exert their effects by inhibiting serotonin (5-HT) re-uptake. Although blockade occurs almost immediately, the neurochemical effects on 5-HT, as measured by in vivo microdialysis, have been a matter of considerable debate. In particular, literature reports yield conflicting neurochemical results in the rat frontal cortex. Thus, while some groups consistently find increases in extracellular 5-HT levels following acute SSRI administration, others reproducibly report an absence of these acute serotonergic effects. In an attempt to unravel this apparent discrepancy, we combined published literature with in-house microdialysis experiments. When we plotted the lateral stereotaxic coordinate of the dialysis probe against published reports on the acute effects of fluoxetine a clear correlation was revealed. Whereas pronounced increases in SSRI-induced 5-HT were observed when the dialysis probe was placed 0 to 1 mm from the midline, effects diminished when the lateral probe placement was greater than 3 mm from the midline. In-house microdialysis studies corroborated these reports. Overall, these results illustrate - for the first time - that the midline stereotaxic coordinate is critical for interpreting the acute serotonergic effects of SSRIs within the frontal cortex. Moreover, the common observation that the clinical efficacy of SSRIs is not evident following acute administration complements preclinical microdialysis results in the lateral frontal cortex. The significance of this observation, along with potential explanations for the disparate neurochemical findings in the medial versus lateral cortices, will be discussed.

Microsensors for in vivo Measurement of Glutamate in Brain Tissue.

Several immobilized enzyme-based electrochemical biosensors for glutamate detection have been developed over the last decade. In this review, we compare first and second generation sensors. Structures, working mechanisms, interference prevention, in vitro detection characteristics and in vivo performance are summarized here for those sensors that have successfully detected brain glutamate in vivo. In brief, first generation sensors have a simpler structure and are faster in glutamate detection. They also show a better sensitivity to glutamate during calibration in vitro. For second generation sensors, besides their less precise detection, their fabrication is difficult to reproduce, even with a semi-automatic dip-coater. Both generations of sensors can detect glutamate levels in vivo, but the reported basal levels are different. In general, second generation sensors detect higher basal levels of glutamate compared with the results obtained from first generation sensors. However, whether the detected glutamate is indeed from synaptic sources is an issue that needs further attention.

Changes in endothelial cell specific molecule 1 plasma levels during preeclamptic pregnancies compared to healthy pregnancies.

OBJECTIVE: We aimed to assess the levels of endothelial cell specific molecule 1 (ESM-1) during pregnancy and preeclampsia. METHODS: Plasma and placental samples were collected from women with a control pregnancy, early- or late-onset preeclamptic women and non-pregnant women (experiment 1). Plasma samples were collected between weeks 12 and birth from pregnant women at high risk for developing preeclampsia (experiment 2). ESM-1 plasma levels were measured by ELISA and in the placenta mRNA and protein were detected by immunohistochemistry and qPCR. RESULTS: In the first experiment we observed lower concentrations of ESM-1 in pregnant women as compared to non-pregnant women and higher concentrations during early- and late-onset preeclampsia as compared to control pregnancies of the same gestational age. Early- and late-onset preeclamptic pregnancies were not different from their subsequent controls in ESM-1 mRNA or protein levels in placental tissue. The second experiment showed that in women who had an control pregnancy, plasma ESM-1 levels were decreased as compared to non-pregnant women, from week 16 ±â€¯2 until the end of pregnancy and returned to non-pregnant levels postpartum. In women who developed early- or late-onset preeclampsia, plasma ESM-1 was also decreased as compared to non-pregnant women from week 20 ±â€¯2 until week 28 ±â€¯2 of pregnancy. Then ESM-1 levels increased and were no longer different from levels in non-pregnant women on weeks 32 and 36. CONCLUSIONS: Plasma ESM-1 levels are decreased during pregnancy and increased in early- and late-onset preeclampsia. The source of ESM-1 is probably not the placenta, but most likely maternal endothelial cells.

Augmentation of SSRI effects on serotonin by 5-HT2C antagonists: mechanistic studies.

The treatment of depression may be improved by using an augmentation approach involving selective serotonin reuptake inhibitors (SSRIs) in combination with compounds that focus on antagonism of inhibitory serotonin receptors. Using microdialysis coupled to HPLC, it has recently been shown that the systemic co-administration of 5-HT(2C) antagonists with SSRIs augmented the acute effect of SSRIs on extracellular 5-HT. In this paper, we have investigated the mechanism through which this augmentation occurs. The increase in extracellular 5-HT was not observed when both compounds were locally infused. However, varying the route of administration for both compounds differentially revealed that an augmentation took place when the 5-HT(2C) antagonist was locally infused into ventral hippocampus and the SSRI given systemically, but not when systemic 5-HT(2C) antagonist was co-administered with the local infusion of citalopram. This suggests that the release of extracellular serotonin in ventral hippocampus may be controlled by (an)other brain area(s). As 5-HT(2C) receptors are not considered to be autoreceptors, this would implicate that other neurotransmitter systems are involved in this process. To investigate which neurotransmitter systems were involved in the interaction, systemic citalopram was challenged with several glutamatergic, GABA-ergic, noradrenergic, and dopaminergic compounds to determine their effects on serotonin release in ventral hippocampus. It was determined that the involvement of glutamate, norepinephrine, and dopamine in the augmentation did not seem likely, whereas evidence implicated a role for the GABA-ergic system in the augmentation.

Effect of increased serotonin levels on [18F]MPPF binding in rat brain: fenfluramine vs the combination of citalopram and ketanserin.

[18F]MPPF is a selective serotonin-1A (5-HT1A) receptor antagonist and may be used to measure changes in the functional levels of serotonin (5-HT). The technique is based on the assumption that the injected radiolabeled ligand competes for the same receptor as the endogenous transmitter. Results from studies using serotonergic ligands are not always consistent. The aim of the present study was to investigate if [18F]MPPF binding is decreased after an increase in 5-HT levels. [18F]MPPF binding was assessed in conscious rats using ex vivo autoradiography. We studied the effect of the 5-HT-releasing agent and reuptake inhibitor fenfluramine (10 mg/kg i.p.) and of a combination of the selective serotonin reuptake inhibitor (SSRI) citalopram (10 micromol/kg, s.c.) with the 5-HT2C antagonist ketanserin (100 nmol/kg, s.c). The effect of both treatments on extracellular 5-HT levels was determined using microdialysis. Fenfluramine treatment resulted in a 30-fold increase in extracellular 5-HT levels in the ventral hippocampus and induced a significant reduction of [18F]MPPF binding in the frontal cortex, hypothalamus, amygdala, and hippocampus. The microdialysis results showed a 10-fold 5-HT increase in the ventral hippocampus after combined administration of ketanserin and citalopram. The combination, however, did not affect [18F]MPPF binding. Our data show that [18F]MPPF binding in conscious rats is only reduced after substantial and therefore nonphysiological increases in 5-HT levels. These results may imply that the majority of 5-HT1A receptors is in the low-affinity state, in vivo.

Differences in the effects of 5-HT(1A) receptor agonists on forced swimming behavior and brain 5-HT metabolism between low and high aggressive mice.

RATIONALE: Male wild house-mice genetically selected for long attack latency (LAL) and short attack latency (SAL) differ in structural and functional properties of postsynaptic serotonergic-1A (5-HT(1A)) receptors. These mouse lines also show divergent behavioral responses in the forced swimming test (FST, i.e., higher immobility by LAL versus SAL mice). OBJECTIVES: We investigated whether the line difference in 5-HT(1A) receptors is associated with a difference in brain 5-HT metabolism, and whether acute administration of a 5-HT(1A) receptor agonist could differentially affect the behavioral responses of LAL and SAL mice. METHODS: 5-HT and 5-hydroxyindoleacetic acid (5-HIAA) levels were measured in homogenates of several brain regions using high-performance liquid chromatography. The behavioral effect of the full 5-HT(1A) receptor agonist, 8-OH-DPAT, and of the somatodendritic 5-HT(1A) autoreceptor agonist, S-15535, was examined in the FST. The effect of 8-OH-DPAT on forced swimming-induced 5-HT metabolism in brain homogenates was determined. RESULTS: In most brain regions, 5-HT and 5-HIAA levels and 5-HT turnover were not significantly different between LAL and SAL mice. 8-OH-DPAT abolished the behavioral line difference in the FST by reducing immobility in LAL mice and reducing climbing in SAL mice. S-15535 induced a similar behavioral effect to 8-OH-DPAT in SAL mice, but did not alter the behavior of LAL mice. Compared with LAL, forced swimming elicited in SAL mice a higher brain 5-HT turnover, which was potently attenuated by 8-OH-DPAT. CONCLUSIONS: It is unlikely that the difference in 5-HT(1A) properties between LAL and SAL mice is an adaptive compensatory reaction to changes in 5-HT metabolism. Although unspecific motor effects, at least in SAL mice, cannot be ruled out, it is suggested that the behavioral effects of 8-OH-DPAT and S-15535 may be mediated by predominant activation of postsynaptic 5-HT(1A) receptors in LAL mice and by presynaptic 5-HT(1A) receptors in SAL mice.

Galantamine-induced behavioral recovery after sublethal excitotoxic lesions to the rat medial septum.

Clinical trials show beneficial effects of acetylcholinesterase (AChE) inhibitors, including galantamine, on cognitive functions in patients with mild to moderate Alzheimer's disease. Galantamine shows a dual action profile by also acting as an allosteric modulator of nicotinic acetylcholine receptors. Nevertheless, its in vivo mechanism of action is only partly understood. Here, we first established a novel lesion model provoking significant functional impairment of the septo-hippocampal projection system without triggering massive neuronal death in the rat medial septum. Next, we studied whether galantamine, administered in doses of 1 and 3mg/kg post-lesion, promotes functional recovery of spatial navigation behaviors, and affects the output of septal cholinergic projections. Infusion of N-methyl-d-aspartate (NMDA; 30nmol/1microl) in the medial septum resulted in spatial learning deficits associated with significant shrinkage of cholinergic neurons and reduced AChE activity in the hippocampus at 7 days post-lesion. Galantamine treatment alone significantly increased the hippocampal acetylcholine concentration and attenuated the NMDA-induced spatial learning impairment. Galantamine post-treatment also affected NMDA-induced changes in AChE and choline-acetyltransferase activities. In conclusion, our data show that galantamine attenuates experimentally-induced cognitive impairments underscored by mild neuronal damage.